Ways Improve Quality of Carburized Quenching Parts and Gas Soft Nitriding Parts

Carburizing and quenching parts, gas soft nitriding parts quality requirements are getting higher and higher. This paper only focuses on the discussion of the process, wish: the use of world-class equipment, only the use of world-class technology, in order to produce world-class products. I think the first - class indicators: carburizing or carbon - nitrogen co - carburization as an example. Surface hardness HRC61 above (HV1 conversion), non-ma ≤3 meters (shallow corrosion), product surface brightness, no carbon black, carbide extremely dispersion. Martensite tissue 1-2, residual A8% below, minimal deformation, no teeth grinding or very little teeth grinding. Sulfide, oxide < 1, same furnace, same steel size, same shape and size product hardness fluctuation ±1HRC.

How to improve the quality of carburized and hardened parts

1. Surface hardness and non-martensite structure of carburized and hardened parts (1) :

In the surface layer of carburized and quenched parts, continuous or discontinuous reticular or blocky black tissue often appears, which happens not to be the area with the greatest surface compressive stress. It has been recognized that it is due to internal oxidation and poor alloying elements that cause the formation of troostite structure, also known as non-martensite structure. Once such a structure is formed, the result is a reduction in surface hardness and wear resistance as well as fatigue limits. Therefore, most of the well-known domestic and foreign vehicle manufacturers have clear regulations on the thickness of non-markov body layer. For example, berte, mercedes-benz and BMW require that the thickness of this layer should be less than 3 meters.

The non-reasons are:

Carburizing out to grinding teeth: grinding teeth will be compressive stress into tensile pressure.

(2) shot peening strengthening, the compressive stress in the high-speed rotation of heat attenuation. Not without grinding teeth? Not grinding teeth is a hot topic in modern gear production. Chongqing qingshan industrial co., LTD. (3.7) is a manufacturer that adopts multi-purpose furnace to produce gear without grinding teeth. Shorten carburizing time, carbide extreme dispersion to save a lot of machining costs, leading: any advanced country in the world.

1.1.1 about non-martensite tissues

The non-martensite structure of carburized and quenched parts includes ferrite formed by surface decarbonization, troostite formed by surface layer along grain boundary, and bainite in some steel types. Diagram 1 of the relationship between the structure layer of the non-martensite and the carbon content of the steel surface. The carbon content on the surface of the workpiece with this kind of structure gradually increases from the surface to the inside, and then gradually decreases to the core after the highest value. The position corresponding to the maximum carbon content is also the place of the maximum compressive stress after quenching.

1.1.2 scope of non-martensite tissues: in the carburizing process, due to internal oxidation, the carbon content on the surface of the carburizing body decreases and produces non-martensite tissues, such tissues as incipient ferrite, incipient troostite (connected into a piece called black belt, not connected into a piece called black net), and bainite of some steel types. All of them were non-martensite. 

FIG. 1: relationship between non-martensite microstructure layer and surface carbon concentration in carburized and quenched steel

Ways Improve Quality of Carburized Quenching Parts and Gas Soft Nitriding Parts

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